Method and apparatus for improving cpap patient compliance

ABSTRACT

A method of operating a device for treating sleep disordered breathing (SDB), wherein the device provides continuous positive airway pressure during sleep, includes applying a treatment pressure to a patient, monitoring the patient for speech output, generating a signal in response to detected speech of the patient, and, in response to the signal, reducing the treatment pressure applied to the patient.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Australian Application No.AU2005903089, filed Jun. 14, 2005, Australian Application No.AU2005906122, filed Nov. 4, 2005, and Australian Application No.AU2005906193, filed Nov. 8, 2005, each of which is incorporated hereinby reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to mechanical ventilation of sleep disorderedbreathing (SDB), and in particular to methods and apparatus forimproving patient compliance in Continuous Positive Airway Pressure(CPAP) treatment.

2. Description of Related Art

A comprehensive background discussion of mechanical ventilation can befound in “Principles and Practice of Mechanical Ventilation” (1994)edited by Martin J Tobin, published by McGraw-Hill Inc., ISBN0-07-064943-7.

The use of nasal Continuous Positive Airway Pressure (CPAP) to treatObstructive Sleep Apnea (OSA) was invented by Colin Sullivan, see U.S.Pat. No. 4,944,310. Generally, the treatment involves providing a supplyof air or breathable gas from a blower to a patient via an air deliveryconduit and a patient interface, such as a full-face or nasal mask, ornasal prongs. While treatment is effective, some patients find ituncomfortable. Improving patient comfort and compliance is a continuingchallenge.

One way to improve comfort is to provide a more comfortable patientinterface. In this regard, the ResMed MIRAGE™ masks have providedsignificant improvement in comfort. See U.S. Pat. Nos. 6,112,746;6,357,441; 6,581,602; and 6,634,358. A more recent development is theResMed MIRAGE™ ACTIVA™ mask series. See International Patent ApplicationWO 2001/97893.

In the early days of nasal CPAP systems for treating OSA, patients werefirst titrated in a clinical study to determine an optimal treatmentpressure. Titration involves a patient sleeping overnight in a clinicand being tested with a mask and CPAP device. The treatment pressureprovided by the CPAP device is adjusted until apneas are eliminated. Thetreatment pressure is usually in the range of 4-20 cmH₂O. A device wouldbe set to that pressure and given to the patient to take home. Asubsequent development was the automatically adjusting device that apatient could take home. The automatically adjusting device will raiseand/or lower the treatment pressure based on indications of obstructivesleep apnea, such as snoring. Such CPAP devices are sometime genericallyreferred to as Automatic Positive Airway Pressure (APAP) devices. SeeU.S. Pat. Nos. 5,245,995; 6,398,739; and 6,635,021.

Another type of nasal CPAP device provides a first pressure duringinhalation (sometimes termed an IPAP) and a second, lower pressureduring exhalation (sometimes termed an EPAP). Examples of these includethe ResMed VPAP™ series, and the Respironics BIPAP series. Bilevel CPAPdevices may be prescribed for patients who do not comply with singlepressure CPAP devices. Some patients perceive that the lower pressureduring exhalation is more comfortable, at least while they are awake.

Another way of improving patient comfort and compliance is to start eachtherapy session at a low therapeutic pressure, e.g., 4 cmH₂O, and rampup to full therapeutic pressure over the first hour, to allow thepatient to adjust to the sensation while falling asleep. Alternatively,the device may set to implement a time delay before full therapeuticpressure is applied, to allow the patient time to fall asleep beforefull therapeutic pressure is applied. See U.S. Pat. Nos. 5,199,424 and5,522,382.

Another form of automatically adjusting CPAP device is the ResMedAUTOSET™ SPIRIT™ device. In this device, the CPAP pressure isautomatically increased or decreased in accordance with indications offlow limitation, such as flow flattening, snore, apnea and hypopnea. SeeU.S. Pat. Nos. 5,704,345; 6,029,665; 6,138,675; and 6,363,933. Anadvantage of an automatically adjusting system is that over time thetreatment pressure required may vary for a particular patient and acorrectly functioning automatic system can obviate the need for thepatient to return for a subsequent sleep study. These patents alsodescribe a method and apparatus for distinguishing between so-called“central” and obstructive apneas.

The contents of all of the aforesaid patents are incorporated bycross-reference.

Some OSA patients find treatment with the above devices uncomfortableand they become non-compliant with the therapy. Other patients such ascardiovascular patients with Congestive Heart Failure, patients with REMHypoventilation, and patients with Respiratory Insufficiency could alsobenefit from a more comfortable and/or effective form of therapy.

One hurdle in patient compliance occurs in the initial stages oftreatment, where a patient may have difficulty in adjusting to thesensations of the therapy and may quit therapy before realizing thebenefits of the therapy.

A further hurdle to patient acceptance of the therapy is in the initialfitting of the patient interface (e.g., mask), where the mask fit istested under relatively low pressure and high flow. This may result innoisy operation of the device and high flow air leaks as the mask isadjusted to the patient, which can be a noisy and unsettling initialexperience for the patient.

Other impediments to patient comfort and compliance include thetreatment impeding the ability of the patient to communicate to theclinician or bed partner, or the patient or bed partner being disturbedby air leaks from the mask.

SUMMARY OF THE INVENTION

One aspect of the invention relates to a method and apparatus toovercome or ameliorate one or more of these disadvantages.

‘Easy Speak’

A first aspect of the invention relates to a method of operating adevice for treating sleep disordered breathing (SDB), wherein saiddevice provides continuous positive airway pressure during sleep, themethod comprising:

applying a treatment pressure to a patient;

monitoring the patient for speech output;

generating a signal in response to detected speech of the patient; and

in response to said signal, reducing the treatment pressure applied tothe patient.

In an embodiment, in response to the signal the treatment pressure isreduced for a predetermined period of time.

In one embodiment, the monitoring the patient includes sensing soundsmade by the patient and analyzing the sounds to detect speech. Theanalysis may include filtering of the sounds to remove non-speech sound.

In another embodiment, the monitoring the patient includes detectingexpiration patterns indicative of speech. The monitoring of the patientmay include detecting pressure and/or flow signals by the device,filtering these signals to remove those indicative of snoring andanalyzing the filtered signals.

In another form, the monitoring of the patient includes sensing ofsounds made by the patient and detection of the arousal state of thepatient. For example, patient sounds made while the patient is awake maybe identified as speech.

In a further form, the monitoring of the patient includes monitoringsounds made by the patient within a predetermined time from the start ofa therapy session. The function may be disabled after the predeterminedtime from the start of the session.

In one form, the speech includes humming.

Alternatively, monitoring the patient may include detecting vibrationindicative of speech, for example by detecting the vocal cord vibrationon the patient's neck.

A further aspect of the invention relates to a method of operating adevice for treating sleep disordered breathing (SDB), wherein saiddevice provides continuous positive airway pressure during sleep, themethod comprising:

applying a treatment pressure to a patient;

monitoring the patient for speech output;

generating a signal in response to detected speech of the patient; and

in response to said signal, controlling one or more functions of thedevice.

In this form, monitoring the patient includes checking the speechagainst one or more vocal commands programmed into the device,recognizing a match between the speech and a vocal command andcontrolling a function of the device associated with the vocal command.

In one form, monitoring the patient compensates for changes in speechcharacteristics due to application of treatment pressure, optionally bydetecting speech characteristics which are less affected by theapplication of treatment pressure.

Another aspect of the invention relates to a method of operating adevice for treating sleep disordered breathing (SDB), wherein saiddevice provides continuous positive airway pressure during sleep, themethod comprising:

applying a treatment pressure to a patient;

monitoring the patient for speech output;

generating a signal in response to detected speech of the patient; and

in response to said signal, reducing the treatment pressure applied tothe patient for a predetermined period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings facilitate an understanding of the variousembodiments of this invention. In such drawings:

FIG. 1 illustrates a ventilator apparatus according to an embodiment ofthe present invention for implementing methods according to embodimentsof the invention;

FIG. 2 is a flowchart illustrating an acclimatization therapy for newusers of CPAP treatment according to an embodiment of the invention;

FIG. 2A is a flowchart of an acclimatization therapy for new CPAP usersaccording to another embodiment of the invention;

FIG. 3 is a flowchart illustrating a method of control of the CPAPtherapy to facilitate speech by the patient during treatment accordingto an embodiment of the invention;

FIG. 3A is a flowchart of a modification of the method of FIG. 3,including detection and execution of voice activated commands accordingto an embodiment of the invention;

FIG. 4 is a graph of a mask pressure against blower set pressure,showing mask leak; and

FIG. 5 is a flowchart illustrating mask leak control according to anembodiment of the invention.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS Hardware

A positive airway pressure (PAP) device in accordance with an embodimentof the invention includes a blower and blower-controller. The blower candeliver a supply of air at positive pressure 2-40 cmH₂O, but generallyin the range of 4-20 cmH₂O to a patient interface via an air deliveryconduit.

The device also includes a flow sensor to measure the flow of air alongthe conduit, and pressure sensors to measure the pressure of air at theblower outlet.

In one form, the device alternatively includes an additional pressuresensor to detect the pressure in the patient interface.

For example, FIG. 1 illustrates a ventilator device according to anembodiment of the invention. As illustrated, the ventilator device mayinclude a servo-controlled blower 2, a flow sensor 4 f, pressure sensor4 p, a mask 6, and an air delivery conduit 8 for connection between theblower 2 and the mask 6. Exhaust gas is vented via exhaust 13.

Mask flow may be measured by a flow sensor, such as a pneumotachographand differential pressure transducer to derive a flow signal F(t).Alternatively, the pneumotachograph may be replaced by a bundle of smalltubes aligned in parallel with the flow from the blower with thepressure difference measured by the differential pressure transduceracross the bundle.

Mask pressure is preferably measured at a pressure tap using a pressuretransducer to derive a pressure signal P_(mask)(t). The pressure sensor4 p and flow sensor 4 f have been shown only symbolically in FIG. 1since it is understood that those skilled in the art would understandhow to measure flow and pressure.

Flow F(t) and pressure P_(mask)(t) signals are sent to a controller ormicroprocessor—referred to herein as processor 15—to derive a pressurerequest signal P_(Request)(t). The controller or processor is configuredand adapted to perform the methodology described in more detail herein.The controller or processor may include integrated chips, a memoryand/or other instruction or data storage medium to implement the controlmethodology. For example, programmed instructions with the controlmethodology are either coded on integrated chips in the memory of thedevice or loaded as software. As those skilled in the art willrecognize, analogue devices may also be implemented in the controlapparatus.

The controller or processor 15 is further adapted to derive parametersindicative of the patient's breathing and sleep pattern, such as forderiving indications of flow limitation, such as flow flattening, snore,apnea and hypopnea and the Apnea Hypopnea Index (AHI), and fordistinguishing between REM and non-REM sleep. See U.S. Pat. Nos.5,704,345 and 6,029,665.

The apparatus of FIG. 1 includes other sensors, communication interfacesand displays, a servo, etc., and functional blocks the details of whichare not necessary for an understanding of the present invention.

Acclimatization Therapy for First Time Users

FIG. 2 illustrates an acclimatization therapy for new users of CPAPtherapy according to an embodiment of the invention.

After initial set up by a clinician, including setting of a fulltherapeutic pressure (step 201), the patient is sent home with a CPAPmask and blower.

For the first few nights of the acclimatization therapy (e.g., two ormore nights), the patient is provided with a headgear and mask fromwhich the elbow and gas conduit have been disconnected, thus allowingthe patient to first become accustomed to the feel of the mask andheadgear during sleep, without additional impediments such as the noiseand air pressure generated by the blower (step 202).

For the next step in the acclimatization therapy, the elbow and gasconduit are connected to the mask, and the blower is turned on.

The blower is set to a “first timer mode” (also referred to herein as a“Max Ramp” or “AccliMATE” mode), in which the treatment pressure for theentire first CPAP session is provided at a sub-therapeutic pressure, forexample at 2 cmH₂O (step 203).

Before the start of the second CPAP session, a series of pre-programmedpatient and/or bed partner feedback questions are displayed on themachine display, the responses to which are used in setting thetreatment pressure for the next session. For example, the patient may beasked to provide a yes/no answer, or a rating out of ten, to questionsrelating to treatment comfort, and the patient and/or the bed partnermay be asked to respond to questions relating to patient restlessnessand sleep quality.

If the patient and/or bed partner responses are sufficiently favorableto indicate that the patient is adjusting to the sensations of thetherapy, and the recorded measurements of the treatment session indicatesubstantial patient compliance with the therapy (steps 204 and 205), thepressure for the next session is incrementally increased (step 206),e.g., by 1 cmH₂O. If the responses do not indicate patientacclimatization, or if other indicators of patient compliance for thesession are negative (for example indicating that the patient removedthe mask for a substantial period) (steps 204 and 205), the treatmentpressure is not increased (step 207), e.g., pressure unchanged.

The pressure is set for the next therapy session (step 208), and theprocess of patient feedback and incremental increase in treatmentpressure is repeated until full therapeutic pressure is reached, e.g.,after 7 or more sessions (step 209). In the case of APAP treatment, oncethe treatment pressure reaches a therapeutic pressure of 4 cmH₂O, thetreatment pressure may be a capped maximum pressure for the session. Inthe case of bilevel CPAP treatment, either just the inhalation (IPAP)pressure may be capped or both the IPAP and the exhalation (EPAP)pressure may be scaled down correspondingly.

If more than a predetermined number of successive—or cumulative—negativefeedback responses are recorded, the controller will cause display of amessage advising the patient to contact the clinician. If the device isconnected to external communication, e.g., to the telephone network, thenotification may be sent directly to the clinician, e.g., data loggedand clinician notified (step 210).

Details of the patient feedback responses, and the treatment pressuresmay be stored in the controller for later review by the clinician.

In an embodiment, the controller may be programmable by the clinicianusing the menu system to alter the parameters of the ‘first timer’ mode,for example, to set the initial therapy session pressure and/or thedaily pressure increment according to the severity of the patient'ssleep disordered breathing and the clinician's opinion of how long thepatient may take to acclimatize to the sensations of the CPAP therapy.

The acclimatization therapy thus allows the patient to gradually adjustto the sensations of CPAP therapy, with the progression profile of theacclimatization controlled according to patient feedback. It is expectedthat adoption of this approach will increase the chance of patientcompliance during the early stages of therapy, and therefore increaselong-term acceptance and compliance.

FIG. 2A illustrates a modified form of acclimatization therapy for firsttime CPAP users, which is adapted to help in setting of an appropriatemaximum treatment pressure.

In the embodiment of FIG. 2A, the clinically-derived full therapeuticpressure for the patient is determined by the clinician in a titrationstudy (step 201A).

In the acclimatization therapy, the CPAP device includes a ‘Max Ramp’feature which is programmed to hold a maximum pressure for apreprogrammed day number (step 209A) and monitor the patient'srespiratory events via the device's monitoring capabilities, such as theResTraxx™ function of ResMed machines to see if that pressure is thecorrect one. Steps 202A-207A are similar to steps 203-207, and 210 ofFIG. 2 described above. The maximum pressure is incrementally increasedeach day until a preset percentage or pressure differential from thetitrated maximum pressure is reached (step 208A), and is held there(step 215A) or increased (step 214A) based on monitored treatmenteffectiveness, the presence/absence of respiratory events, clinicianreview, or may be based upon user/bed partner feedback, comfort andcompliance (steps 210A, 211A, 212A) such as that illustrated in FIG. 2.Once maximum pressure is reached (step 213A) and/or therapy sessionindicates successful treatment (step 212A), the therapeutic pressure isfixed (step 216A) and data logged and clinician notified (step 217A).

For example, a new CPAP patient may be titrated in a sleep study and amaximum treatment pressure of 12 cmH₂O may be prescribed. On the firstnight of treatment the treatment ramps from 4 to 5 cm over the first 45minutes of treatment. On the next night the pressure ramps up over 45minutes from 5 cm to 6 cm and so on until it gets to within apredetermined amount—for example 4 cmH₂O— or a predeterminedpercentage—such as 80%—of the prescribed maximum treatment pressure. Soin this example the CPAP machine may be programmed by the clinician tostop the daily increase at a pressure of 8 (i.e., 12-4) cmH₂O for a setnumber of days (e.g., up to 7 days) to monitor the patient airway usingthe monitoring functions of the CPAP machine. If the patient is nothaving adverse respiratory events at say the pressure of 10 cm, then themaximum treatment pressure may be fixed at that level rather thanprogressing to the originally-prescribed level of 12. If the patient isstill having adverse respiratory events at a pressure of 12, then themachine may increase it or refer the patient to the clinician for adecision on whether to increase the treatment pressure.

It is envisaged that this acclimatization therapy would give at leastsome of the benefits of the AutoSetting function of an AutoSet CPAPmachine but resulting in a fixed pressure that many Doctors/Cliniciansare comfortable with rather than AutoSetting adjustment of the treatmentpressure breath-by-breath. This keeps greater control of the setpressure in the hands of the clinician, which some patients andclinicians may be more comfortable with. This acclimatization may alsobe used as a stepping stone to getting patients and cliniciansaccustomed to AutoSetting functions.

In the flowchart of FIG. 2A, those items in bold may be preset orprescribed by the clinician (e.g., initial sub-therapeutic pressure,increment pressure, max pressure, pre-limit or % of max pressure, X no.of days to hold at pre-limit or % of max pressure, no. of events orother criteria that indicates successful treatment). Those boxes indashed lines may optionally be omitted.

Possible advantages of the acclimatization therapy of FIG. 2A includeimprovement in the treatment of patients where the prescribed pressureis too high or too low, with consequent reduction in therapist's timetreating those patients. Such patients currently take a substantialamount of therapist's time for treatment because they are being overtreated or under treated and furthermore these patients are often nothappy/compliant. The stair stepping approach of the ‘Max Ramp’ featurecould cut the costs of treatment of such patient by helping todetermining the appropriate pressure with minimal therapistintervention. The method may be carried out with modifications based ona ResMed Elite machine or a ResMed ResTraxx machine, both of which areless expensive machines than one having full AutoSet capabilities. Ifthe prescribed pressure was determined to be wrong, the home medicalequipment (HME) provider could send the patient a card to change thepressure; simple and cost effective. Also, the method includes minimalwork from the patient, which helps to achieve new patient compliance andacceptance of the treatment.

A further embodiment of the invention provides a simplifiedacclimatization therapy (“Max ramp”) mode with greater control by theclinician.

In this embodiment, the machine is programmable to increase the maximumtreatment pressure automatically over time. The Clinician could programthe start pressure, say 4 cm, and have the device ramp up to theprescribed pressure over a set period of time with no patientinvolvement.

For example, start pressure may be set at 4 cm and maximum pressure setat 10. The clinician could prescribe a Max Ramp of 6 days. On Day 1 thedevice would start at 4 cm and stay at 4 cm all night. On day 2 thedevice would start at 4 and ramp, depending on the set ramp time (max 1hour), to 5 cm and stop. Day 3 start at 4 cm and ramp to 6 cm, and so onuntil the set maximum therapeutic pressure is reached.

The clinician would choose the number of days the Max ramp was to occurand the device would calculate the daily increase in a linear or otherpredetermined fashion. Alternatively the clinician could set the startpressure and start Max Ramp feature. For example, start pressure 4 cmand stop at the start Max Ramp Feature of 7 cm, max pressure=12 cm. Inthis scenario, day one the device would start at 4 cm, ramp to 7 cm overthe ramp time (max 1 hour) then hold there for the first night. On day 2the device would start at 4 cm, ramp (max 1 hour) to 8 cm (or what everthe linear calculation says, and stop) and so on throughout the set timefor the Max Ramp.

Optionally, the clinician could choose a machine mode which allows thepatient to hold at a pressure for an additional night if the patientfeels the pressure is becoming too much. This could be accomplished bypressing a sequence of buttons on the device. This machine mode alsoallows programming by the clinician to set boundary conditions on theacclimatization therapy (“Max ramp”) mode.

For example, the machine display may prompt the patient at the end ofeach daily session to enter a response indicating how they coped withthe therapy. The patient could press “Okay” or “Not okay”. If manysubsequent days are “okay”, the machine increases the daily rampincrement to ramp to prescribed maximum therapy pressure moreaggressively, thus bringing the patient to therapy as early as possible.If the patient responses indicate that the patient is struggling toacclimatize to therapy (e.g. two consecutive days of “Not Okay”), thedaily ramp increment is decreased to extend the acclimatization period,within the clinician-set boundaries.

More than a preset number of daily “Not okays” may cause the device toprompt the patient with help details (visual and/or audible methods)and/or request patient to contact clinician before getting toofrustrated with the therapy, thus potentially reducing drop-outs evenfurther. Where the device has communication capabilities, the device mayalso contact the clinician directly to get into contact with thepatient.

Further details of the process phases, the machine modes and an exampleof this embodiment are set out below.

A. Acclimatization Process Phases:

-   -   The acclimatization therapy goes through three phases:    -   1. Initiation Phase: Physician or Clinician prescribes an        “AccliMATE” mode    -   2. AccliMATE Phase: the AccliMATE mode automatically adjusts        nightly CPAP pressure until final set-point CPAP pressure is        reached according to physician or clinician    -   3. Standard CPAP Phase: Flow Generator Operates in Standard CPAP        mode

B. AccliMATE Mode Detail:

-   -   1. Physician/Clinician Adjustable Parameters:    -   (a) Adjustment period (settable range): 1-30 days    -   (b) End target CPAP setting (‘T’): 4-20 cm H2O    -   (c) Starting night #1 CPAP setting (“S”): 4-*H2O (can only be        set where “S”<“T”)    -   (d) Optional patient “snooze” button function. When pressed by        the patient this would maintain previous day's CPAP pressure        setting for a physician/clinical set limited number of days at        any individual pressure. Settable range=0-5 days. This snooze        function can be turned off or can allow the patient to remain at        any one pressure for a limited number of days if they push the        “snooze” button at the beginning of the next night's session        during the CPAP AccliMATE phase.        Note: standard nightly ramp from 4 cm H₂O to that night's set        point can be set as normal from 0-45 minutes using standard ramp        function    -   2. Machine calculation modes:        -   (a) Linear        -   (b) Logarithmic        -   (c) Exponential        -   (d) Step-function (0.5 cm/day, 1 cm/day, 2 cm/day, 3 cm/day,            etc.)        -   (e) Other formulae

C. Example:

-   -   Clinician/Physician sets:    -   (a) Adjustment period=7 days    -   (b) End target CPAP=0 cm H2O    -   (c) Starting CPAP=4 cm H2O    -   (d) Patient Snooze=0 days (i.e., off)

Day # 1 2 3 4 5 6 7 CPAP 4 cm H₂O 5 cm H₂O 6 cm H₂O 7 cm H₂O 8 cm H₂O 9cm H₂O 10 cm H₂O

Easy Speak

A further embodiment of the invention, illustrated in FIG. 3,facilitates verbal communication by the patient to a clinician or bedpartner during treatment.

At the commencement of the therapy session (step 301), the session timerof the controller is started (step 302), and the ‘easy speak’ mode ofthe blower is activated step (step 303).

In this mode, the controller is adapted to determine speech by thepatient (step 304). Such detection may be, for example, by means of amicrophone (not shown) at the patient interface, connected back to thecontroller, with filtering or signal processing means adapted todistinguish between frequencies and patterns indicative of the sounds ofspeech rather than of snoring, or by detection of expiration patterns orother breathing patterns typical of speech. By combining thepressure/microphone signal (or some signal derived from it) and the flowor rate of change of flow, more accurate speech detection may bepossible.

One means of implementing the determination of speech is to employ voicerecognition technology, which is in itself well known in other fieldssuch as in hands-free typing software and mobile telephones. Voicerecognition technology allows a distinction to be made between speech bya particular person and other sounds and other people speaking withinthe same environment. Other developments in distinguishing between typesof sounds include the technology employed in noise-canceling headphones,such as those developed by Bose Corporation of USA.

The device may be programmed to recognize certain vocal commands spokenby the patient, and upon matching the vocal commands to its programmedvocabulary of words will implement an associated control function of thedevice. For example, the machine may be ‘trained’ to recognize thepatient speaking the words “stop” to stop the flow generator, “start” torestart, and “talk” to implement the speech mode as described below. Inthis way, the machine may be controlled.

Upon detection of speech by the patient, the pressure provided by theblower is temporarily reduced or stopped for a first predetermined time(step 305), for example of 5-60 seconds, or more preferably during theentire period of detected speech, thus allowing the patient to speakwithout the resisting pressure. If within this time the patient ceasesto speak for a second predetermined period (for example, 2 to 5seconds), the treatment pressure may be resumed, or gradually increased(step 306). In Autoset® devices, the pressure may be resumed at theminimum pressure. Also, the treatment pressure resumes unchanged ifspeech is not detected by easy speak mode (step 310).

By reducing the treatment pressure when the patient is attempting tospeak, the sensation—which some patients find discomforting—of airrushing out as the patient speaks is minimized, and communication withthe patient's bed partner and/or family or with the clinician becomeseasier. It is believed that this will make the therapy easier to adjustto and reduce another impediment to patient compliance with the therapy.

To reduce the possibility of false positive detection of speech, and theundue interruption of therapy that this may cause, the controller isprogrammed to turn off the easy speak mode (step 308) once a certaintime of the therapy session has elapsed (step 307). If desired, thistime period may be selectable by the patient via the set up menu of theblower, within certain limits. For example, the patient may be able toinput a time of 15 to 60 minutes, depending on how long it willtypically take that patient to fall asleep. The set up menu of themachine may also allow the patient turn off the easy speak modealtogether. After easy speak mode is turned off, the therapy sessioncontinues at full therapeutic pressure (step 309).

Where the flow generator is of the type in which the treatment pressureis ramped up over a 5 to 20 minute period at the beginning of eachtreatment session, the ‘easy speak’ mode may be activated only duringthat initial period in which the pressure is being increased, anddisabled once the flow generator reaches full therapeutic pressure.

The easy speak mode may also be activated when the device is set to afitting mode, so that patient communication to the clinician is improvedwhen the mask is being fitted.

Instead of, or in addition to, the illustrated embodiment in which thecontroller uses the session timer to control whether the easy speak modeis activated, it is possible to use other indicators of the patient'ssleep state to activate the easy speak when the patient is awake.

For example, the controller may detect that the patient is awake bydetection of ventilation levels, respiratory rates or breathing patternsrepresentative of a waking state or by a level detector which detectsthat the patient is sitting up.

Alternatively, the blower control may respond to signals or derivedindices indicative of sleep by switching off the ‘easy speak’ mode. Forexample, rapid eye movement (“REM”) is a readily detectable indicationof a certain phase of sleep, and slow-wave sleep may also be detected.

Alternatively, the easy speak mode may remain in standby mode for theentire duration of the treatment session and activate whenever sleep isdetected by the patient. Some patients may naturally talk during sleep,and the easy speak mode may still serve to reduce patient arousal ordisturbance by reducing the air flow out of the mouth during suchsleep-talking.

In one embodiment, the apparatus includes a microphone to pick up thevoice of a patient. This microphone may be incorporated into the flowgenerator (with its electrical interface) or may be independent from theflow generator and have a cable to connect to the flow generator. Thiswould allow the microphone to be situated on the flow generator, mask,tube, or even bedding or bed. Preferably, the microphone is in the airchannel and part of the tube or independent connector so that it doesnot need replacing with different masks or other components.

FIG. 3A illustrates a modification of the method of FIG. 3, includingvoice activation of commands.

Steps 301A-310A are similar to steps 301-310 of FIG. 3 described above.Upon reducing the treatment pressure (at step 305A), the machine isprogrammed to detect recognized voice commands from the user occurringwithin a predetermined time (step 311A), for example 2 to 60 seconds. Ifno such command is detected, the treatment pressure is resumed (at step306A) as per FIG. 3. If however a recognized voice command is detectedwithin the preset time, the processor will carry out the command (step312A), optionally provide a response to the user (step 313A)—such as anaudible, tactile or visual response—and continue voice command detectionfor the predetermined time. If no further voice commands are detected,the treatment pressure will be resumed (at step 306A).

In order to detect talking and lower the pressure ready for speech orvoice commands, an in-line pressure sensor at the flow generator couldbe used.

This may be similar to the snore sensor used for the current ResMed S8Autoset machine. The sensor may be any type of microphone sensor but inone embodiment may be a pressure or flow sensor such as apiezo-resistive or capacitive pressure sensor mounted at theflow-generator outlet as per our snore sensor. A fast response time ispreferred, for example around 1 ms response, the signal may be amplifiedand filtered. Preferably, a frequency bandwidth which incorporates thatof higher frequency speech is used, however for the control of pressureto allow speech and possibly simple commands a bandwidth of 30-200 Hzsuch as that in the Autoset snore signal may be sufficient.

In order to assist the differentiation between snore and speech, thelikelihood that speech will be on the expiration component of the cyclecan be used, also snore is more likely (but not always) to be oninspiration. Thus, detection of speech may be limited to the expirationpart of the respiratory cycle.

In any event, as previously stated, the Easy speak feature is preferablydisabled after the ramp period, and during the ramp period it isunlikely that the patient will snore. Also, the Easy speak option ispreferably switched on only after the ‘smartstart’ feature (U.S. Pat.No. 6,240,921) is switched off.

Other identifying features of speech which may be used to distinguishspeech from snore are the waveform, amplitude and non-repetitive natureof speech.

As speech generally occurs on expiration, a further mitigating featurethat could be used is the lowering of EPR (expiration pressure) onlywhen speech is detected, and employing continued inspiratory pressuresupport with a fast pressure rise time. Thus, in the event of a falsepositive detection of speech, treatment is not withdrawn on inspiration.

Especially when a nasal mask is used, the component phonemes of thepatient's speech are altered by the mouth leak caused by application ofthe treatment pressure, and the voice recognition system preferably hascapability to compensate for this. For example, the recognition may giveemphasis to those characteristics of speech which are less affected bythe treatment pressure (such as stress, rhythm and pitch) or to processthe sound to identify and restore the lost speech elements.Alternatively, or in addition, the voice recognition may be programmedto recognise alternative forms of the commands both with and without theapplication of the treatment pressure.

With a nasal mask, in order to activate the Easy speak function, hummingmay be used to produce a pressure signal at the flow generator if thisis to be used rather than a mask or tube mounted pressure signal ormicrophone, in order to ensure sufficient signal when flow is exitingthe mouth. In any event, humming may be a good way to trigger thetreatment pressure to be lowered, prior to talking or voice commandsoccurring. In this way, the treatment pressure may be reduced prior totalking, and the sometimes unpleasant sensation of talking with a nasalmask on may be avoided.

Where a full face mask is used, the sensation of talking with the maskon is not as unpleasant, and either humming or talking may be used asthe trigger for the Easy speak and voice command functions.

In another embodiment, an Easy speak algorithm may detect speech andthen drop the pressure, e.g., to 4 cmH₂O, for a period of time, e.g., 5seconds. The 5 second timeout is reset every time speech is detected.Thus, the pressure remains low until 5 seconds after the patient stopstalking. This algorithm may be implemented on existing devices, e.g.,ResMed's S8 Autoset. For example, the algorithm may be implemented as apure software solution. Thus, no electrical or mechanical modificationsare necessary.

Inputs to the algorithm include the flow generator output flow and thesnore signal. The snore signal may be a low pass filtered absolute valueof the high pass filtered pressure, similar to the “rms” of the ACpressure signal.

In the algorithm, the derivative of the flow is calculated. There may bea number of filters in the calculation of the snore, which may cause thesnore signal to be delayed. Therefore, the flow derivative may be alsodelayed in order to facilitate timing of the threshold comparisons. Forexample, the delay in an implementation may be 31 samples whichcorresponds to 310 ms.

In an embodiment, Easy speak may be triggered by two methods. The firstmay be patient humming which causes a relatively large snore signal. Thesecond may be the assumption that when using a nasal mask, when you openyour mouth to speak, a sudden rush of air is released from the mouth.This corresponds to a large positive flow derivative.

The algorithm checks these signals against empirically determinedthresholds and Easy speak is activated when these signals are above thethresholds. So, if the snore signal is relatively loud (e.g., due tohummming) or the flow derivative and snore signal are high, Easy speakis triggered.

For example:

If (snore > SNORE_THRESHOLD_HUMMING) then Easy speak triggered Else if((snore > SNORE_THRESHOLD) AND (flow_derivative > FLOW_DERIVE_THRESHOLD)then Easy speak triggered End

Exemplary empirically derived constants are shown in the below chart.The chart shows the magnitude of the difference between the thresholds.

Constant Value Used in SNORE_THRESHOLD_HUMMING 1000 “Humming” detectionSNORE_THRESHOLD 100 Open mouth speech FLOW_DERIVE_THRESHOLD 20 Openmouth speech

The combination of the flow derivative and snore signal may be usedbecause flow noise by breathing/leak is of similar magnitude to thenormal speech signal. This may need to be modified for a full-face maskas there is not the sudden rush of air from the mouth when speaking.

Mask Leak Control

In a further embodiment of the invention, described with reference toFIGS. 4 and 5, the response of the blower to changes indicative ofexcessive air leakage at the patient interface is controlled forimproved patient comfort and compliance and reduced possibility ofdisturbance.

FIG. 4 is a schematic graph of mask pressure against flow generatorpressure illustrating mask leak where the mask is not sitting properlyand sealing completely on the patient's face, for example where the maskand headgear has not been optimally adjusted or where the patient mayhave partially dislodged the mask during sleep.

With reference to FIG. 4, the blower set pressure is on the x axis andthe mask pressure on they axis.

It can seen that the pressure lost due to mask leak is the verticaldistance between the mask pressure curve and the 45° line. In a typicalsituation, the mask leak at lower blower pressures will be approximatelylinear with blower pressure, but above a certain blower pressure willbegin to depart more significantly from the blower pressure as theincreased pressure causes a significant increase in mask leakage. Thepoint at which this departure commences, and the gradient of thisdeparture, will depend on the type and fit of the mask to the patient,and may also vary from one session to the next, or within a therapysession, depending on the patient's sleeping position.

In prior art APAP machines, air leakage at the mask is detected by adrop in the mask pressure, and the response of the blower as governed bythe controller is to increase the blower pressure to compensate.However, in some instances this increased pressure merely serves tofurther reduce the sealing of the mask onto the patient's face, and theincreased pressure is wholly or largely lost by increased leakage. Insuch instances, the volume of air being leaked is increased with littleor no net benefit to efficacy of the therapy, and with increased chanceof arousal of or disturbance to the patient and/or the bed partner.

In the present embodiment of the invention, the response of the blowerto detection of mask leak is modified.

FIG. 5 is a flowchart illustrating the steps of the mask leak controlmethod according to an embodiment of the invention.

At first detection of excessive mask leak (step 501), for example asdetermined by low mask pressure, by an excessive differential betweenthe blower pressure and the pressure at the mask or by a computed maskimpedance parameter below a certain threshold, the blower controllercauses an increase in the blower pressure (step 502) to compensate forthe leak and maintain the therapeutic pressure to desired levels, thusmoving further to the right along the mask pressure curve of FIG. 4.

Another determination of mask pressure is made (step 503) and, if theincreased blower pressure has corrected the mask pressure to compensatefor the leakage then the higher blower pressure is continued (step 504).The patient continues to be monitored for arousal (step 505).

If however the increased blower pressure has resulted in less than apredetermined pressure increase in the mask, or a greater thanpredetermined flow volume increase, this means that the blower isoperating at a low-gradient part of the mask pressure curve of FIG. 4.In this case, the controller is programmed to then recognize that thepressure increase has wholly, or mostly, been ineffectual due toincreased leakage at the mask.

When detecting this condition, the controller is programmed to thenreduce the blower pressure (step 506) (for example, by a set percentageof the treatment pressure or to the ramp start pressure) or to inhibitfurther increases in the flow generator output pressure.

The mask leak threshold against which the increased mask leak iscompared (step 508) may be a fixed quantity or proportion, for examplewhere a 2 cmH₂O increase in blower results in less than a 1 cmH₂Opressure increase at the mask.

Alternatively, the mask leak threshold may vary as a function of apatient sleep phase indicator so that a greater amount of mask leakageis tolerated if the patient is in a heavier phase of sleep and thus lesslikely to be disturbed, or if other indicators of disturbance of thepatient—such as respiratory rate—remain low. Indicators of sleep phaseare known per se in sleep medicine and include monitoring of brain wavesand/or respiration.

In a further alternative form of this embodiment, the mask leakthreshold may vary as a function of indications of flow limitation, suchas flow flattening, snore, apnea and hypopnea, or the Apnea HypopneaIndex (AHI), so that a greater amount of mask leakage is tolerated ifthe patient is more in need of higher treatment pressure. The blowercontroller is preferably programmable by the clinician to adjust themask leak threshold, or turn off the mask leak control function, forpatients with historically high flow limitation measurements.

By reducing or capping the blower set pressure in circumstances of highmask leakage, rather than increasing the pressure further as was done inthe prior art, disturbance of the patient and/or bed partner by thenoise or air flow caused by excessive air leakage is minimized. Whilethe therapy may continue at sub-optimal pressure, it may continue toprovide some airway support and is considered that this may in manyinstances be preferable to waking the patient or having the patientremove the mask during sleep. The former is a substantial patientcomfort and compliance issue and the latter may deny the patient theentire benefit of the therapy.

Furthermore, by reducing the blower set pressure in response toexcessive mask leak, the mask may settle back into improved conformitywith the patient's face and the mask leakage be reduced, thus alteringthe mask pressure curve shown in FIG. 4 to one closer to the 45° line.

The controller may be programmed to make one or more further attempts toramp up blower pressure after a predetermined time periods, for example15 minutes, have elapsed to reassess the quality of the mask-to-patientseal.

The controller may also be programmed to monitor in real time thepatient's AHI and other patient arousal and flow limitation indicators,to detect any reduction in effectiveness of therapy at the lowerpressure. If the indicators show increased flow limitation and/orpatient arousal at the lower treatment pressure, indicative ofinsufficient treatment pressure for airway stability, the controllerwill re-increase the blower pressure (step 507).

Patient arousal may also be sensed by monitoring body positions.Continual movement, if detected in conjunction with high leak, mayindicate patient arousal due to mask leak.

Snoring is indicative of airway narrowing, and may be used as anindicator that the treatment pressure is too low and must be increasedregardless of leak.

In essence, this embodiment seeks to apply the lowest pressure requiredto treat the patient effectively and limits maximum pressure incircumstances of mask leak, whereas previous treatments did only theformer. In this way, a balance is achieved between patient arousal dueto mask leak and effectiveness of the treatment, to help maintainpatient compliance with the therapy.

The controller keeps a record of incidents where the blower pressure isreduced in response to excessive mask leak, for subsequent review by theclinician to help with mask selection and adjustment for the patient.

Also, at the end of a session where excessive mask leak has beendetected, the controller may cause to be displayed on the machine amessage alerting the patient to the need to adjust the fit of the mask,and/or to contact the clinician.

The CPAP machine may have two leak control modes, and controls forselecting between these modes depending for example on patientpreference and compliance levels. In a first of these modes, which forexample may be selected for less compliant patients, the machine ondetection of a leak reduces the treatment flow/pressure and maintainsthe pressure at a below full-therapeutic to allow the mask to sealagainst the patient's face.

In the second mode of the leak control method, the flow/pressure isreduced to a sub-therapeutic pressure for a brief predetermined period,for example 15-60 seconds, to allow the mask to reseal against thepatient's face, and then is ramped back up to therapeutic pressure.

In a further embodiment, a mask seal testing and mask fitting regimen isprovided wherein the mask is fitted to the patient in a clinical settingand the device switched to a “mask fitting” operational mode. In thismode, the flow generator is controlled to apply a normal range treatmentpressure, with the flow rate limited to a flow approximately equal to orslightly above the vent flow rate for the mask.

If the mask seals well, the pressure at the mask will be at or near fulltherapeutic pressure. If there is a substantial mask leak, this may bedetected by insufficient pressure in the mask, without the noisyoperation and large volume air leaks which the prior art lowpressure-high volume mask fitting modes regimens. In this way, the maskfit may be adjusted without undue noise and a large volume of air flowrushing past the patient's face, and a further hurdle to patientadoption of and compliance with the therapy is reduced.

In this specification, the word “comprising” is to be understood in its“open” sense, that is, in the sense of “including”, and thus not limitedto its “closed” sense, that is the sense of “consisting only of”. Acorresponding meaning is to be attributed to the corresponding words“comprise, comprised and comprises where they appear.

While the invention has been described in connection with what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the invention. Also, the various embodiments described abovemay be implemented in conjunction with other embodiments, e.g., aspectsof one embodiment may be combined with aspects of another embodiment torealize yet other embodiments. In addition, while the invention hasparticular application to patients who suffer from OSA, it is to beappreciated that patients who suffer from other illnesses (e.g.,congestive heart failure, diabetes, morbid obesity, stroke, barriatricsurgery, etc.) can derive benefit from the above teachings. Moreover,the above teachings have applicability with patients and non-patientsalike in non-medical applications.

1. A method of operating a device for treating sleep disorderedbreathing (SDB), wherein said device provides continuous positive airwaypressure during sleep, the method comprising: applying a treatmentpressure to a patient; monitoring the patient for speech output;generating a signal in response to detected speech of the patient; andin response to said signal, reducing the treatment pressure applied tothe patient.
 2. The method according to claim 1, wherein reducing thetreatment pressure includes reducing the treatment pressure for apredetermined period of time.
 3. The method according to claim 2,wherein reducing the treatment pressure includes reducing the treatmentpressure for 5-60 seconds.
 4. The method according to claim 1, whereinmonitoring the patient includes sensing sounds made by the patient andanalyzing the sounds to detect speech.
 5. The method according to claim4, wherein analyzing the sounds includes filtering the sounds to removenon-speech sound.
 6. The method according to claim 1, wherein monitoringthe patient includes monitoring expiration patterns indicative ofspeech.
 7. The method according to claim 1, wherein monitoring thepatient includes detecting pressure and/or flow signals by the device,filtering these signals to remove those indicative of snoring andanalyzing the filtered signals.
 8. The method according to claim 1,wherein monitoring the patient includes sensing sounds made by thepatient and detecting an arousal state of the patient.
 9. The methodaccording to claim 1, wherein monitoring the patient includes monitoringsounds made by the patient within a predetermined time from the start ofa therapy session.
 10. The method according to claim 9, whereinmonitoring the patient includes monitoring sounds made by the patientwithin 2-60 seconds from the start of a therapy session.
 11. The methodaccording to claim 9, wherein detection of speech is disabled after thepredetermined time from the start of the therapy session.
 12. The methodaccording to claim 1, wherein the speech includes humming.
 13. Themethod according to claim 1, wherein monitoring the patient includesdetecting vibration indicative of speech.
 14. The method according toclaim 13, wherein detecting vibration includes detecting vocal cordvibration on the patient's neck.
 15. A method of operating a device fortreating sleep disordered breathing (SDB), wherein said device providescontinuous positive airway pressure during sleep, the method comprising:applying a treatment pressure to a patient; monitoring the patient forspeech output; generating a signal in response to detected speech of thepatient; and in response to said signal, controlling one or morefunctions of the device.
 16. The method according to claim 15, whereinmonitoring the patient includes checking the speech against one or morevocal commands programmed into the device, recognizing a match betweenthe speech and a vocal command, and controlling a function of the deviceassociated with the vocal command.
 17. The method according to claim 15,wherein monitoring the patient includes compensating for changes inspeech characteristics due to application of treatment pressure.
 18. Themethod according to claim 17, wherein compensating for changes in speechcharacteristics includes detecting speech characteristics which are lessaffected by the application of treatment pressure.
 19. A method ofoperating a device for treating sleep disordered breathing (SDB),wherein said device provides continuous positive airway pressure duringsleep, the method comprising: applying a treatment pressure to apatient; monitoring the patient for speech output; generating a signalin response to detected speech of the patient; and in response to saidsignal, reducing the treatment pressure applied to the patient for apredetermined period of time.
 20. The method according to claim 19,wherein reducing the treatment pressure includes reducing the treatmentpressure to 4 CmH2O.
 21. The method according to claim 19, wherein thepredetermined period of time is 5 seconds.
 22. The method according toclaim 19, further comprising resetting the predetermined period of timeevery time speech is detected.
 23. The method according to claim 19,wherein monitoring the patient includes detecting humming.
 24. Themethod according to claim 19, wherein monitoring the patient includesdetecting a flow derivative.
 25. A PAP device for carrying out themethod of claim 1.